1. Field of the Disclosure
The present disclosure is directed to a piston for use in diesel and other internal combustion engines, and more particularly, a piston comprising two pieces precision cast of steel or similar materials and friction-welded into a complete piston.
2. Description of Related Art
Present diesel and other high performance internal combustion engines are being operated at extremely high combustion pressures and temperatures. For example, many on- and off-road diesel applications operate with diesel fuel injection at pressures in excess of 30,000 psi and exhaust gas turbo-charging which can create intake manifold pressures in excess of 50 psi. In addition, government mandated exhaust emission standards in developed countries and markets including, but not limited to, the United States, Japan, and the EEC require strict control of the combustion processes and strict control of emissions in service, as well as specific performance and emissions control longevity of the engines during on-road, off-road, and marine applications.
The foregoing conditions have resulted in multiple strategies employed to cool the pistons of such engines, the most common of which is to precisely inject substantial amounts of engine oil into chambers formed in the pistons to remove combustion heat.
Presently known piston designs, which are commercially practiced, do not adequately address several extremely critical aspects of piston manufacturing and performance including but not limited to the foregoing. For example, current piston designs struggle to obtain proper dimensional attributes to generally maintain required operational and long-term durable performance of the piston to cylinder bore sealing rings at presently required operating temperatures and pressures as well as minimizing combustion gas blow-by and resultant increased exhaust emissions without costly and extensive machining operations and other additional manufacturing steps. Additionally, current piston designs have problems incorporating an integral reservoir for cooling oil into the piston crown area with adequate volume and highly consistent piston-to-piston volume without the incorporation of separate sealing dams or rings that are mechanically attached to the piston in various manners, all of which require additional machining and manufacturing steps to prepare the piston to accept the separate sealing dams or rings, the inserting and fixing of the sealing rings in the manufacturing process, and the separate manufacture of the sealing dams or rings themselves. Further, current piston designs also have problems with the mechanical failure of the cooling oil reservoir dams or rings and/or the failure of the fixing means of such devices to the piston, causing physical separation from the piston and the resulting loss of cooling oil in one or more pistons and introduction of foreign materials into the interior of the engine and subsequent severe engine damage or failure.
The absence of adequate mechanical support of the piston to cylinder bore sealing ring area of typical pistons including, but not limited to, the flexure of the lower parts of the sealing ring areas and the area where the ring sealing area joins the piston crown often results in cracking and failure of such areas of the piston that incorporate the sealing rings and result in severe engine damage or failure. Also, the absence of adequate mechanical support of the sealing ring area of typical pistons results in the reduction and/or loss of sealing ring performance that causes gas blow-by, which leads to lubricating oil infiltration into the combustion chamber and coating the ring lands with partially combusted lube oil in a process termed “coking.” Each of these conditions increases exhaust emissions and/or causes mechanical failure of the sealing rings and severe engine damage or failure.
It is also known in the art to friction weld two or more previously machined parts of a piston together to permit various configurations to be made that would otherwise be commercially impractical or impossible. Typical two-piece pistons consist of a steel forged crown and a separate skirt, usually forged of the same or a compatible steel alloy which guides the piston assembly in the combustion cylinder of an engine. Prior to friction welding the mating surfaces of the crown and skirt, the crown requires extensive and costly machining operations to provide opposing, axially-aligned bores that are configured to accept a steel pin which joins the piston with a connecting rod. This known piston design is configured to provide a heat and pressure resistant steel crown incorporating the sealing rings and an attached lower member comprised of the skirt. The separate pieces presently start out in as-forged or as/rough-cast condition and are subsequently machined to close tolerances prior to joining by way of friction or inertia welding or another suitable method. However, in each of these processes for producing a piston, precision machining the joining or connecting surfaces that are to be welded together is a costly and additional required prior step/operation to prepare the two piston pieces for the friction welding process.
Known two-piece friction welded pistons also incorporate a cooling oil reservoir which can consist of a recess in the piston crown and/or separate reservoirs in the skirt. Alternatively, a reservoir is formed in the crown and is closed off with a plate assembly, wherein the composite reservoirs communicate with oil spray jets located in the engine block to introduce cooling oil to the underside of the piston crown to reduce the operating temperature of the crown and thus prolong piston life and ensure proper operation of the piston to cylinder bore sealing rings.
Such pistons as described above tend to be very heavy and their configurations are limited by the possible need to join three separate parts to form a complete piston: (1) the steel crown and sealing ring groove section, (2) the skirt section by friction welding and (3) the machining of a receptacle for and the mechanical insertion of an oil dam or plate. Similarly, such piston designs often require multiple methods of forming a cooling oil reservoir/gallery including machining and the mechanical insertion of dams or plates to form such reservoirs.
The incorporation of cooling oil reservoirs or galleries in a piston is also commonly known. This is typically done with the employment of separate dams or plates of various materials which are inserted and fixed beneath the crown area. Alternatively, such reservoirs may also be partially incorporated in one or more of the two-piece friction welded pistons by machining such reservoirs in rough castings or rough forgings prior to joining them in a friction welding process.
Other known piston designs are made of rough cast or as-rough forged as one-piece configurations. However, these designs have several disadvantages including the requirement of extensive post-forging or post-casting machining, the absence of a closed oil gallery formed integrally with the crown, and the absence of lateral/axial support of the lower portion of the sealing ring carrying portion of the piston crown. These design and manufacturing limitations result in requiring a separate oil dam inserted in the crown and the absence of axial and radial support to prevent flexure of the sealing ring portion of the piston. This lack of axial and radial support is known to cause premature flexure failures of the piston crown and the degradation of the piston to cylinder bore sealing ring performance during the service life of the piston which can increase the exhaust emissions of an engine so equipped and can result severe engine damage or failure thereof. The flexure of the lower part of the piston which contains the piston to cylinder bore sealing ring grooves leads to the loss of long-term complete sealing between the piston and the cylinder bore seating rings which, in turn, results in higher oil consumption, combustion blow-by, higher operating temperatures, coking, reduction in service life and increased exhaust emissions which can render the operation of the engine unlawful under certain rules and regulations.
In presently employed friction welded pistons comprising a closed oil gallery, three sealing rings are employed; the first and most adjacent to the piston crown is a one piece compression ring which seals the piston to the cylinder bore during the four cycles of operation. The second and next adjacent ring is also a one piece compression ring which complements the first ring and completes the seal of the piston to the cylinder bore in a similar manner. The third ring is an oil scraper ring which comprises one or more parts which function solely to remove the cooling and lubricating oil from between the piston the cylinder wall during each of the piston strokes
In each of the foregoing configurations of pistons, it is critical to provide a means by which lubricating and cooling oil removed by the third ring during the movements of the piston can be immediately returned to the engine crankcase by way of the cylinder bore and through certain interruptions in the cylindrical piston body as described below
Accordingly, there is a need for a piston that facilitates the passage of the foregoing oil to the cylinder bore and thence the engine crankcase after it is wiped and/or scraped from the cylinder wall. There is also a need for a piston that eliminates additional post-casting and/or post-forging machining including but not limited to that which incorporates and/or affixes separate oil reservoir sealing dams. There is also a need for eliminating post-casting and/or post-forging machining of contact or joining surfaces prior to an inertia or friction welding process for joining at least two separate pieces of a piston.